02.Jni开发流程_C/C++调用java
(创建于2017/11/18) c/c++调用Java包括几个分类，调用Java静态和非静态属性，静态和非静态方法四种 提示： 生成一个类中所有属性成员签名的方法如下： 1.进入这个类class文件所在的路径：如JniUtils这个类在d盘下 D:\application\java\eclipse-workspace\TestJni\bin\com\renzhenming\bsdiff> 2.执行命令D:\application\java\eclipse-workspace\TestJni\bin\com\renzhenming\bsdiff>javap -p -s JniUtils 3.会得到结果：descriptor所对应的就是签名 Compiled from "JniUtils.java" public class com.renzhenming.bsdiff.JniUtils { public static int key; descriptor: I static {}; descriptor: ()V public com.renzhenming.bsdiff.JniUtils(); descriptor: ()V public native void changeIntKey(); descriptor: ()V public native void accessMethod(); descriptor: ()V public native void accessStaticMethod(); descriptor: ()V public int getRandomInt(int); descriptor: (I)I public static java.lang.String getUUId(); descriptor: ()Ljava/lang/String; } 生成系统类签名的方法，以java.util.Date为例 直接进入命令行，输入javap -s -p 完整类名 C:\Users\renzhenming>javap -s -p java.util.Date Compiled from "Date.java" public class java.util.Date implements java.io.Serializable, java.lang.Cloneable, java.lang.Comparable<java.util.Date> { private static final sun.util.calendar.BaseCalendar gcal; descriptor: Lsun/util/calendar/BaseCalendar; private static sun.util.calendar.BaseCalendar jcal; descriptor: Lsun/util/calendar/BaseCalendar; private transient long fastTime; descriptor: J private transient sun.util.calendar.BaseCalendar$Date cdate; descriptor: Lsun/util/calendar/BaseCalendar$Date; private static int defaultCenturyStart; descriptor: I private static final long serialVersionUID; descriptor: J private static final java.lang.String[] wtb; descriptor: [Ljava/lang/String; private static final int[] ttb; descriptor: [I public java.util.Date(); descriptor: ()V public java.util.Date(long); descriptor: (J)V public java.util.Date(int, int, int); descriptor: (III)V public java.util.Date(int, int, int, int, int); descriptor: (IIIII)V public java.util.Date(int, int, int, int, int, int); descriptor: (IIIIII)V public java.util.Date(java.lang.String); descriptor: (Ljava/lang/String;)V public java.lang.Object clone(); descriptor: ()Ljava/lang/Object; public static long UTC(int, int, int, int, int, int); descriptor: (IIIIII)J public static long parse(java.lang.String); descriptor: (Ljava/lang/String;)J public int getYear(); descriptor: ()I public void setYear(int); descriptor: (I)V public int getMonth(); descriptor: ()I public void setMonth(int); descriptor: (I)V public int getDate(); descriptor: ()I public void setDate(int); descriptor: (I)V public int getDay(); descriptor: ()I public int getHours(); descriptor: ()I public void setHours(int); descriptor: (I)V public int getMinutes(); descriptor: ()I public void setMinutes(int); descriptor: (I)V public int getSeconds(); descriptor: ()I public void setSeconds(int); descriptor: (I)V public long getTime(); descriptor: ()J private final long getTimeImpl(); descriptor: ()J public void setTime(long); descriptor: (J)V public boolean before(java.util.Date); descriptor: (Ljava/util/Date;)Z public boolean after(java.util.Date); descriptor: (Ljava/util/Date;)Z public boolean equals(java.lang.Object); descriptor: (Ljava/lang/Object;)Z static final long getMillisOf(java.util.Date); descriptor: (Ljava/util/Date;)J public int compareTo(java.util.Date); descriptor: (Ljava/util/Date;)I public int hashCode(); descriptor: ()I public java.lang.String toString(); descriptor: ()Ljava/lang/String; private static final java.lang.StringBuilder convertToAbbr(java.lang.StringBuilder, java.lang.String); descriptor: (Ljava/lang/StringBuilder;Ljava/lang/String;)Ljava/lang/StringBuilder; public java.lang.String toLocaleString(); descriptor: ()Ljava/lang/String; public java.lang.String toGMTString(); descriptor: ()Ljava/lang/String; public int getTimezoneOffset(); descriptor: ()I private final sun.util.calendar.BaseCalendar$Date getCalendarDate(); descriptor: ()Lsun/util/calendar/BaseCalendar$Date; private final sun.util.calendar.BaseCalendar$Date normalize(); descriptor: ()Lsun/util/calendar/BaseCalendar$Date; private final sun.util.calendar.BaseCalendar$Date normalize(sun.util.calendar.BaseCalendar$Date); descriptor: (Lsun/util/calendar/BaseCalendar$Date;)Lsun/util/calendar/BaseCalendar$Date; private static final sun.util.calendar.BaseCalendar getCalendarSystem(int); descriptor: (I)Lsun/util/calendar/BaseCalendar; private static final sun.util.calendar.BaseCalendar getCalendarSystem(long); descriptor: (J)Lsun/util/calendar/BaseCalendar; private static final sun.util.calendar.BaseCalendar getCalendarSystem(sun.util.calendar.BaseCalendar$Date); descriptor: (Lsun/util/calendar/BaseCalendar$Date;)Lsun/util/calendar/BaseCalendar; private static final synchronized sun.util.calendar.BaseCalendar getJulianCalendar(); descriptor: ()Lsun/util/calendar/BaseCalendar; private void writeObject(java.io.ObjectOutputStream) throws java.io.IOException; descriptor: (Ljava/io/ObjectOutputStream;)V private void readObject(java.io.ObjectInputStream) throws java.io.IOException, java.lang.ClassNotFoundException; descriptor: (Ljava/io/ObjectInputStream;)V public static java.util.Date from(java.time.Instant); descriptor: (Ljava/time/Instant;)Ljava/util/Date; public java.time.Instant toInstant(); descriptor: ()Ljava/time/Instant; public int compareTo(java.lang.Object); descriptor: (Ljava/lang/Object;)I static {}; descriptor: ()V } C:\Users\renzhenming> 1.在Java的一个类中，如下，定义各种类型的属性和方法 import java.util.Random; import java.util.UUID; public class JniUtils { public String key = "renzhenming"; private Human human = new Man(); public static int count = 9; public native static String getStringFromC(); public native String getString2FromC(int i); //访问属性，返回修改之后的属性内容 public native String accessField(); public native void accessStaticField(); public native void accessMethod(); public native void accessStaticMethod(); public native void accessNonVirtualMethod(); public native String toChineseString(String value); public native void accessConstructor(); public native void setArray(int [] arr); public native int[] getArray(); public native void cached(); public native static void initIds(); public static void main(String[] args) { String text = getStringFromC(); System.out.println(text); JniUtils t = new JniUtils(); text = t.getString2FromC(6); System.out.println(text); System.out.println("key修改前："+t.key); t.accessField(); System.out.println("key修改后："+t.key); System.out.println("count修改前："+count); t.accessStaticField(); System.out.println("count修改后："+count); t.accessMethod(); t.accessStaticMethod(); System.out.println("访问构造方法"); new JniUtils().accessConstructor(); System.out.println("访问被子类重写后的父类方法"); new JniUtils().accessNonVirtualMethod(); System.out.println(new JniUtils().toChineseString("想乱码的日子里")); int arr [] = {12,3,43,55,44,1,566}; new JniUtils().setArray(arr); for(int i = 0 ; i < arr.length;i++ ) { System.out.println(arr[i]); } System.out.println("-------------------------------"); int [] jarr = new JniUtils().getArray(); for(int i = 0 ; i < jarr.length;i++ ) { System.out.println(jarr[i]); } System.out.println("-------------------------------"); new JniUtils().createGlobalRef(); System.out.println(new JniUtils().getGlobalRef()); new JniUtils().deleteGlobalRef(); //释放了再获取就会空指针 //System.out.println(new JniUtils().getGlobalRef()); try { new JniUtils().exception(); } catch (Exception e) { System.out.println("发生异常："+e.getMessage()); } //不断调用cached方法 for (int i = 0; i < 100; i++) { t.cached(); } } //产生指定范围的随机数 public int genRandomInt(int max){ System.out.println("genRandomInt 执行了..."); return new Random().nextInt(max); } //产生UUID字符串 public static String getUUID(){ return UUID.randomUUID().toString(); } //加载动态库 static{ System.loadLibrary("JniTest");//这是生成的dll动态库的名字 initIds(); } } //类Human和类Man代码如下（测试jni调用父类方法而设置）： public class Human { public void sayHi() { System.out.println("人打招呼"); } } public class Man extends Human{ public void sayHi() { System.out.println("男。。。。。人打招呼"); } } 2.创建native方法，使用javah生成头文件 /* DO NOT EDIT THIS FILE - it is machine generated */ #include "jni.h" /* Header for class com_dongnaoedu_jni_JniTest */ #ifndef _Included_com_renzhenming_bsdiff_JniUtils #define _Included_com_renzhenming_bsdiff_JniUtils #ifdef __cplusplus extern "C" { #endif /* * Class: _com_renzhenming_bsdiff_JniUtils * Method: getStringFromC * Signature: ()V */ JNIEXPORT jstring JNICALL Java_com_renzhenming_bsdiff_JniUtils_getStringFromC (JNIEnv *, jclass); JNIEXPORT jstring JNICALL Java_com_renzhenming_bsdiff_JniUtils_getString2FromC (JNIEnv *, jobject, jint); JNIEXPORT jstring JNICALL Java_com_renzhenming_bsdiff_JniUtils_accessField (JNIEnv *, jobject); JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_accessStaticField (JNIEnv *, jobject); JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_accessMethod (JNIEnv *, jobject); JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_accessStaticMethod (JNIEnv *, jobject); JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_accessConstructor (JNIEnv *, jobject); JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_accessNonVirtualMethod (JNIEnv *, jobject); JNIEXPORT jstring JNICALL Java_com_renzhenming_bsdiff_JniUtils_toChineseString (JNIEnv *, jobject, jstring); JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_setArray (JNIEnv *,jobject,jintArray); JNIEXPORT jintArray JNICALL Java_com_renzhenming_bsdiff_JniUtils_getArray (JNIEnv *, jobject); JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_localRef (JNIEnv *, jobject); JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_createGlobalRef (JNIEnv *,jobject); JNIEXPORT jstring JNICALL Java_com_renzhenming_bsdiff_JniUtils_getGlobalRef (JNIEnv *, jobject); JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_deleteGlobalRef (JNIEnv *, jobject); JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_exception (JNIEnv *, jobject); #ifdef __cplusplus } #endif #endif 3.将头文件引入as中（jni.h和jni_md.h引入同上次笔记），编写c代码，如下 #define _CRT_SECURE_NO_WARNINGS #include "com_renzhenming_bsdiff_JniUtils.h" #include <string.h> //功能：获取到指定类中一字符串类型成员变量，修改返回得到新的字符串 JNIEXPORT jstring JNICALL Java_com_renzhenming_bsdiff_JniUtils_changeKey (JNIEnv *env, jobject jobj) { //我们编写的native方法是非静态方法，所以这里是jobject，而我们需要jclass来获取fieldid,所以这样转换 jclass clazz = (*env)->GetObjectClass(env, jobj); //参数分别为class对象，属性名，属性签名（签名得到的方法查看文档），获取到我们需要修改的属性的id值 jfieldID fieldId = (*env)->GetFieldID(env, clazz, "key", "Ljava/lang/String;"); //从这个对象jobj中获取这个id fieldid的jstring 对象 jstring jstr = (*env)->GetObjectField(env, jobj, fieldId); //将jni类型jstring 转换为c对象char ,从而我们可以调用c方法修改这个对象的值 char *c_str = (*env)->GetStringUTFChars(env, jstr, JNI_FALSE); //将这个对象的值和text这个字符串连接得到我们需要的新值 char text[30] = "handsome "; strcat(text, c_str); //再次将这个新值对应的c对象char转换为jni类型jstring， jstring new_jstr = (*env)->NewStringUTF(env, text); //将这个jstring类型的新对象设置给这个jobj这个对象中id值为fieldId的这个对象，至此对象值已经被我们修改 (*env)->SetObjectField(env, jobj, fieldId, new_jstr); //删除 (*env)->DeleteLocalRef(env,new_jstr); //返回这个新的字符串，这里没有用到 return new_jstr; } #define _CRT_SECURE_NO_WARNINGS #include "com_renzhenming_bsdiff_JniUtils.h" #include <string.h> //函数实现 JNIEXPORT jstring JNICALL Java_com_renzhenming_bsdiff_JniUtils_getStringFromC (JNIEnv *env, jclass jcls){ return (*env)->NewStringUTF(env,"C String"); } JNIEXPORT jstring JNICALL Java_com_renzhenming_bsdiff_JniUtils_getString2FromC (JNIEnv *env, jobject jobj, jint num){ return (*env)->NewStringUTF(env,"C String2"); } //每个native函数，都至少有两个参数（JNIEnv*,jclass或者jobject) //1）当native方法为静态方法时： //jclass 代表native方法所属类的class对象(JniTest.class) //2）当native方法为非静态方法时： //jobject 代表native方法所属的对象 //基本数据 //Java基本数据类型与JNI数据类型的映射关系 //Java类型->JNI类型->C类型 /* boolean jboolean byte jbyte; char jchar; short jshort; int jint; long jlong; float jfloat; double jdouble; void void */ //引用类型(对象) //String jstring //object jobject //数组,基本数据类型的数组 //byte[] jByteArray //对象数组 //object[](String[]) jobjectArray //C/C++访问Java的成员 //1.访问属性 //修改属性key JNIEXPORT jstring JNICALL Java_com_renzhenming_bsdiff_JniUtils_accessField (JNIEnv *env, jobject jobj){ //我们编写的native方法是非静态方法，所以这里是jobject，而我们需要jclass来获取fieldid,所以这样转换 jclass clazz = (*env)->GetObjectClass(env, jobj); //参数分别为class对象，属性名，属性签名（签名得到的方法查看文档），获取到我们需要修改的属性的id值 jfieldID fieldId = (*env)->GetFieldID(env, clazz, "key", "Ljava/lang/String;"); //从这个对象jobj中获取这个id fieldid的jstring 对象 jstring jstr = (*env)->GetObjectField(env, jobj, fieldId); //将jni类型jstring 转换为c对象char ,从而我们可以调用c方法修改这个对象的值 char *c_str = (*env)->GetStringUTFChars(env, jstr, JNI_FALSE); //将这个对象的值和text这个字符串连接得到我们需要的新值 char text[30] = "handsome "; strcat(text, c_str); //再次将这个新值对应的c对象char转换为jni类型jstring， jstring new_jstr = (*env)->NewStringUTF(env, text); //将这个jstring类型的新对象设置给这个jobj这个对象中id值为fieldId的这个对象，至此对象值已经被我们修改 (*env)->SetObjectField(env, jobj, fieldId, new_jstr); (*env)->DeleteLocalRef(env,new_jstr); //返回这个新的字符串，这里没有用到 return new_jstr; } //访问静态属性 JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_accessStaticField (JNIEnv *env, jobject jobj){ //jclass jclass cls = (*env)->GetObjectClass(env, jobj); //jfieldID jfieldID fid = (*env)->GetStaticFieldID(env, cls, "count", "I"); //GetStatic<Type>Field jint count = (*env)->GetStaticIntField(env, cls, fid); count++; //修改 //SetStatic<Type>Field (*env)->SetStaticIntField(env,cls,fid,count); } //2.访问java方法 JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_accessMethod (JNIEnv *env, jobject jobj){ //jclass jclass cls = (*env)->GetObjectClass(env, jobj); //jmethodID jmethodID mid = (*env)->GetMethodID(env, cls, "genRandomInt", "(I)I"); //调用 //Call<Type>Method jint random = (*env)->CallIntMethod(env, jobj, mid, 200); printf("random num:%ld",random); //..... } //静态方法 JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_accessStaticMethod (JNIEnv *env, jobject jobj){ //jclass jclass cls = (*env)->GetObjectClass(env, jobj); //jmethodID jmethodID mid = (*env)->GetStaticMethodID(env, cls, "getUUID", "()Ljava/lang/String;"); //调用 //CallStatic<Type>Method jstring uuid = (*env)->CallStaticObjectMethod(env, cls, mid); //随机文件名称 uuid.txt //jstring -> char* //isCopy JNI_FALSE，代表java和c操作的是同一个字符串 char *uuid_str = (*env)->GetStringUTFChars(env, uuid, JNI_FALSE); //拼接 char filename[100]; sprintf(filename, "D://%s.txt",uuid_str); //w 打开只写文件，若文件存在则文件长度清为0，即该文件内容会消失。若文件不存在则建立该文件。 FILE *fp = fopen(filename,"w"); fputs("i love jason", fp); fclose(fp); } //访问构造方法（Date 生成一个时间戳） JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_accessConstructor (JNIEnv *env, jobject jobj) { //根据包名得到类，类似反射 jclass cls = (*env)->FindClass(env, "java/util/Date"); //获取类中要获取的方法id(获取构造方法，方法名传"<init>") jmethodID methodid = (*env)->GetMethodID(env, cls, "<init>", "()V"); //实例化一个对象，类似反射 jobject date_obj = (*env)->NewObject(env, cls, methodid); //通过这个对象调用getTime方法，需要获取到这个方法的id jmethodID g_methodid = (*env)->GetMethodID(env, cls, "getTime", "()J"); //执行这个方法,返回值是long类型，所以CallLong jlong time = (*env)->CallLongMethod(env, date_obj, g_methodid); //占位符用的lld，是long long类型的，如果直接用ld占位符打印，打出的是负数 printf("\ntime:%lld\n", time); (*env)->DeleteLocalRef(env,date_obj); } //访问父类被子类重写的方法 JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_accessNonVirtualMethod (JNIEnv *env, jobject jobj) { //在java中，父类指向子类对象，调用被子类重写的方法，执行的是子类的方法，在jni中 //我们可以调用到父类的方法 jclass cls = (*env)->GetObjectClass(env, jobj); //获取类中human属性(先获取到id) 对象的签名 jfieldID fid = (*env)->GetFieldID(env, cls, "human", "Lcom/renzhenming/bsdiff/Human;"); jobject human_obj = (*env)->GetObjectField(env, jobj, fid); //获取父类class jclass human_class = (*env)->FindClass(env, "com/renzhenming/bsdiff/Human"); //获取父类中需要调用的方法的methodid jmethodID s_mid = (*env)->GetMethodID(env,human_class,"sayHi","()V"); //执行指定方法 //子类方法 (*env)->CallObjectMethod(env, human_obj, s_mid); //父类方法（c++中要重写父类方法，用的是virtual关键字）（调用父类方法传入的class不能通过 //GetObjectClass从human_obj中获取，因为这样获取到的是子类的class） (*env)->CallNonvirtualObjectMethod(env, human_obj, human_class, s_mid); } //解决jni中文乱码的问题 JNIEXPORT jstring JNICALL Java_com_renzhenming_bsdiff_JniUtils_toChineseString_ (JNIEnv *env, jobject jobj, jstring jstr) { //输出 //char *c_str = (*env)->GetStringUTFChars(env, in, JNI_FALSE); //printf("%s\n",c_str); //c -> jstring char *c_str = "马蓉与宋江"; //char c_str[] = "马蓉与宋喆"; //jstring jstr = (*env)->NewStringUTF(env, c_str); //执行String(byte bytes[], String charsetName)构造方法需要的条件 //1.jmethodID //2.byte数组 //3.字符编码jstring jclass str_cls = (*env)->FindClass(env, "java/lang/String"); jmethodID constructor_mid = (*env)->GetMethodID(env, str_cls, "<init>", "([BLjava/lang/String;)V"); //jbyte -> char //jbyteArray -> char[] jbyteArray bytes = (*env)->NewByteArray(env, strlen(c_str)); //byte数组赋值 //0->strlen(c_str)，从头到尾 //对等于，从c_str这个字符数组，复制到bytes这个字符数组 (*env)->SetByteArrayRegion(env, bytes, 0, strlen(c_str), c_str); //字符编码jstring jstring charsetName = (*env)->NewStringUTF(env, "GB2312"); //调用构造函数，返回编码之后的jstring return (*env)->NewObject(env, str_cls, constructor_mid, bytes, charsetName); } //-----------------------操作数组涉及到数组的同步问题（ReleaseIntArrayElements）-----------------------------// //操作传入的数组 JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_setArray (JNIEnv *env, jobject jobj, jintArray array) { //jintArray ->jint指针->c int数组 jint *elems = (*env)->GetIntArrayElements(env, array, JNI_FALSE); //数组的长度 int len = (*env)->GetArrayLength(env, array); //排序（传入的compare类似Java中的比较器） qsort(elems, len, sizeof(jint), compare); //将排序结果同步到Java中的数组 //最后一个参数 mode //0 表示Java数组进行更新，并且释放c/c++数组 //JNI_ABORT 表示Java数组不更新，释放c/c++数组 //JNI_COMMIT 表示Java数组进行更新，但不释放c/c++数组 (*env)->ReleaseIntArrayElements(env, array, elems, 0); } //返回一个数组 JNIEXPORT jintArray JNICALL Java_com_renzhenming_bsdiff_JniUtils_getArray (JNIEnv *env, jobject jobj) { //创建一个指定大小的数组 jintArray jint_arr = (*env)->NewIntArray(env, 10); //获取到数组指针 jint *elems = (*env)->GetIntArrayElements(env, jint_arr, NULL); int i = 0; for ( ; i< 10; i++) { elems[i] = i; } //同步 (*env)->ReleaseIntArrayElements(env, jint_arr, elems, 0); return jint_arr; } //局部引用 JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_localRef (JNIEnv *env, jobject jobj) { int i = 0; for (; i < 5; i++) { //创建对象，以Date为例 jclass cls = (*env)->FindClass(env, "java/util/Date"); jmethodID constructor_id = (*env)->GetMethodID(env, cls, "init", "()V"); jobject obj = (*env)->NewObject(env, cls, constructor_id); //.... //不在使用这个对象了需要回收 (*env)->DeleteLocalRef(env, obj); //.... } } //创建全局引用(共享，可以跨多个线程) jstring global_str; JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_createGlobalRef (JNIEnv *env, jobject jobj) { jstring jstr = (*env)->NewStringUTF(env,"jni is a bitch"); global_str = (*env)->NewGlobalRef(env, jstr); } //获取全局引用 JNIEXPORT jstring JNICALL Java_com_renzhenming_bsdiff_JniUtils_getGlobalRef (JNIEnv *env, jobject jobj) { return global_str; } //删除全局引用 JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_deleteGlobalRef (JNIEnv *env, jobject jobj) { (*env)->DeleteGlobalRef(env, global_str); } //Java捕获c异常（如果不做抛异常处理，直接再Java层try是抓不到异常信息的） JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_exception (JNIEnv *env, jobject jobj) { jclass cls = (*env)->GetObjectClass(env, jobj); jfieldID fid = (*env)->GetFieldID(env, cls, "value2", "Ljava/lang/String;"); //检测是否发生Java异常 jthrowable exception = (*env)->ExceptionOccurred(env); if (exception != NULL) { //让Java代码可以继续运行 //清空异常信息 (*env)->ExceptionClear(env); //补救措施 fid = (*env)->GetFieldID(env, cls, "value", "Ljava/lang/String;"); } //获取属性值 jstring jstr = (*env)->GetObjectField(env, jobj, fid); char *str = (*env)->GetStringUTFChars(env, jstr, NULL); //对比属性是否合法 if (stricmp(str, "renzhenming") != 0) { //抛出异常，给Java处理 jclass newExcCls = (*env)->FindClass(env, "java/lang/IllegalArgumentException"); (*env)->ThrowNew(env, newExcCls, "key's value is invalid!"); } } //静态缓存 //static jfieldID key_id JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_cached(JNIEnv *env, jobject jobj){ jclass cls = (*env)->GetObjectClass(env, jobj); //»ñÈ¡jfieldIDÖ»»ñÈ¡Ò»´Î //¾Ö²¿¾²Ì¬±äÁ¿ static jfieldID key_id = NULL; if (key_id == NULL){ key_id = (*env)->GetFieldID(env, cls, "key", "Ljava/lang/String;"); printf("--------GetFieldID-------\n"); } } //加载动态库的时候就初始化全局变量，再loadLibrary后调用 jfieldID key_fid; jmethodID random_mid; JNIEXPORT void JNICALL Java_com_renzhenming_bsdiff_JniUtils_initIds(JNIEnv *env, jclass jcls){ key_fid = (*env)->GetFieldID(env, jcls, "key", "Ljava/lang/String;"); random_mid = (*env)->GetMethodID(env, jcls, "genRandomInt", "(I)I"); } 4.生成dll动态库，放到eclipse中调用 public static void main(String[] args) { String text = getStringFromC(); System.out.println(text); JniTest t = new JniTest(); text = t.getString2FromC(6); System.out.println(text); System.out.println("key修改前："+t.key); t.accessField(); System.out.println("key修改后："+t.key); System.out.println("count修改前："+count); t.accessStaticField(); System.out.println("count修改后："+count); t.accessMethod(); t.accessStaticMethod(); System.out.println("访问构造方法"); new JniUtils().accessConstructor(); System.out.println("访问被子类重写后的父类方法"); new JniUtils().accessNonVirtualMethod(); System.out.println(new JniUtils().toChineseString("想乱码的日子里")); int arr [] = {12,3,43,55,44,1,566}; new JniUtils().setArray(arr); for(int i = 0 ; i < arr.length;i++ ) { System.out.println(arr[i]); } System.out.println("-------------------------------"); int [] jarr = new JniUtils().getArray(); for(int i = 0 ; i < jarr.length;i++ ) { System.out.println(jarr[i]); } System.out.println("-------------------------------"); new JniUtils().createGlobalRef(); System.out.println(new JniUtils().getGlobalRef()); new JniUtils().deleteGlobalRef(); //释放了再获取就会空指针 //System.out.println(new JniUtils().getGlobalRef()); try { new JniUtils().exception(); } catch (Exception e) { System.out.println("发生异常："+e.getMessage()); } }
